The present invention relates generally to a continuously variable transmission for an automotive vehicle, and more particularly to a diagnostic apparatus capable of monitoring the control arrangement of the transmission to check for correct or normal control of the speed ratio of the transmission.
There has been proposed an automotive vehicle which is equipped with a continuously variable transmission for transmitting the output of its engine to its drive wheels at a steplessly variable speed ratio, and with a shift-regulating device for changing the speed ratio of the transmission and/or rate of variation in the speed ratio in response to command signals from a control system for the transmission. Such an automotive vehicle is capable of continuously varying the speed ratio depending upon the running conditions, and may consequently enjoy improved fuel economy. If desired, the speed ratio of the transmission, or the rate of variation in the speed ratio of the transmission, i.e., the shifting speed may be controlled in response to a variation in an error between the actual speed ratio or engine speed, and its target value. In this case, the shifting operation of the variable transmission is achieved with improved control response (stability).
In such an automotive vehicle, it is required to check the variable transmission and its control system for normal functioning, at the time of maintenance services or upon occurrence of a trouble with the transmission. For this purpose, the individual related components must be checked under various possible operating conditions of the transmission. This procedure is difficult to perform. Therefore, there has been a need to give the vehicle a self-diagnostic function for automatic monitoring and diagnosis of the transmission and the control system.